Polyurethane compositions having stable reactivity

ABSTRACT

The pot life of a polyurethane composition is increased by providing a composition containing a polyisocyanate, polyol, highly dispersed silica, and a filler wherein at least a portion of the filler is coated.

This invention relates to retarded uncatalyzed and catalyzedpolyurethane compositions having stable reactivity and to their use foradhesives, sealants and casting compounds.

BACKGROUND OF THE INVENTION

One-component and multiple-component polyurethane compositions have longbeen used as adhesives, sealants or casting compounds. Theseapplications for polyurethane compositions are reviewed, for example, inChapters 8 and 11 of Kunststoff-Handbuch, 3rd Edition, Vol. 7,Hanser-Verlag, 1993. In the case of two-component systems, one componentgenerally consists of liquid polyhydroxy compounds optionally containingfillers, catalysts and other auxiliaries while the second componentessentially contains a liquid diisocyanate or polyisocyanate either inpure form or as a so-called quasi-prepolymer or in the form of isomermixtures. By virtue of their good adhesion properties on variousmaterials and their high tensile, tensile shear and peel strengths,coupled with very high breaking elongation, these adhesives, sealantsand casting compounds are used in a number of industrial and manualapplications, including for example car manufacture, general utilityvehicle manufacture, ship building and boat building, general machineconstruction, the electrical industry and civil engineering.

In many applications, the steps involved require very long pot liveswhich, in addition, are expected to remain constant over the period forwhich the polyurethane compositions are stored before application.

The pot life of a polyurethane composition is understood to be the timeleft for proper application after complete mixing of a two-component ofmultiple-component system before the viscosity of the mixture becomes sohigh through incipient reaction that the mixture can no longer beproperly applied.

Pot life can be controlled within certain limits through the type andquantity of catalyst used. However, it has not yet been possible for agiven formulation to prolong the reaction and hence the pot life anyfurther without a catalyst. In cases such as these, less reactiveisocyanates had to be used. It has often been proposed in the generalliterature and in the patent literature to retard the uncatalyzedreaction by addition of an acid, cf. for example J. H. Saunders, K. C.Frisch, Polyurethanes, Chemistry and Technology, Vol. 1, Chemistry, page213, Interscience Publ., 1962. For example, the addition of hydrochloricacid or acid chlorides is proposed. However, where this approach isadopted, the reaction is not genuinely retarded, instead all thecatalytically active alkaline impurities in the composition areneutralized. However, the addition of acids to adhesives, sealants orcasting compounds can lead to corrosion on the surfaces of thesubstrates to be bonded or encapsulated so that, in many cases, thismethod cannot be applied.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Not applicable.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, the problem addressed by the present invention was toreduce the reactivity of one-component and, preferably, two-component ormultiple-component polyurethane compositions below the so-called "basicreactivity" of the composition, i.e. below the reactivity which thecomposition has without a catalyst. In addition, the pot life directlyrelated to this reactivity was to remain substantially constantthroughout the storage of the unmixed components.

According to the invention, the solution to this problem ischaracterized in that the one-component or multiple-componentpolyurethane compositions contain

one or more diisocyanates or polyisocyanates,

one or more diols and/or polyols,

highly disperse silicas,

fillers and

optionally other auxiliaries and additives, the fillers being at leastpartly coated.

In the context of the invention, a "highly disperse silica" isunderstood to be a fine-particle, substantially amorphous pyrogenicsilica with an SiO₂ content of more than 99.8% by weight which isobtained, for example, by hydrolysis of silicon tetrachloride in anoxyhydrogen flame. These silicas are commercially available, forexample, under the name of "Aerosil®".

The addition of highly disperse silicas to adhesives, sealants orcasting compounds has long been known and is regarded as standardpractice. Hitherto, silicas have been added with the object of reducingthe sedimentation of fillers in the compositions or to provide thecompositions with thixotropic rheological behavior. In the case ofpaste-like products, however, the addition of Aerosil in accordance withthe prior art is often unnecessary because the rheological properties ofthese products are achieved through the fine-particle fillers.

The use of highly disperse silicas for reducing the reactivity ofpolyurethane systems below their basic reactivity is new and has neverbeen described before. However, the effect of the silicas as a reactionretarder and stabilizer can only be utilized in filler-containingpolyurethane systems if the fillers are at least partly coated.

The highly disperse silicas used are preferably the non-aftertreatedso-called "hydrophilic" silicas which are commercially available withvarious specific surfaces (BET surfaces). The following commercialproducts are mentioned by way of example: Aerosil 380, Aerosil 300,Aerosil 200, Aerosil 150, Aerosil 130.

In addition to hydrophilic silicas, aftertreated so-called "hydrophobic"silicas may also be used for the compositions according to theinvention. Any aftertreated hydrophobic silicas known per se may beused, including for example the silicas aftertreated with dimethylchlorosilane, dimethyl silazane, long-chain chlorosilanes, for exampleoctyl trichlorosilane, or even polydimethyl siloxanes. These silicas arecommercially available, for example, under the names of Aerosil R 202, R805, R 812, R 972, R 974 or CABOSIL N 70-TS.

Suitable fillers are any of the fillers known per se which are widelyused in polyurethane chemistry providing they are at least partlycoated. Examples of suitable fillers are limestone flour, natural groundchalks (calcium carbonates or calcium magnesium carbonates), heavy spar,talcum, mica, clays or even carbon black. The filler must be at leastpartly coated, i.e. generally at least 20% by weight and preferably atleast 30% by weight of the filler should be coated. The coating offillers is known per se, the use of coated fillers being recommended inthe literature to facilitate their dispersion in the polymer matrix.There is no known reference to the effect of the surface coating on thepot life of polyurethane systems.

The coating material may be selected from a large number of compounds.Surface coatings of long-chain saturated or unsaturated fatty acids,particularly stearic acid, and alkali or alkaline earth metal saltsthereof, carboxylated polybutadienes, carboxylated poly-α-olefins, resinacids (abietic acid or derivatives thereof) and/or metal salts and/oresters thereof are mentioned by way of example.

Preferred diols and/or polyols for the binder are liquid polyhydroxycompounds containing two or three hydroxyl groups per molecule, forexample difunctional and/or trifunctional polypropylene glycols withmolecular weights in the range from 200 to 6,000 and preferably in therange from 400 to 3,000. Statistical and/or block copolymers of ethyleneoxide and propylene oxide may also be used. Another group of preferredpolyethers are the polytetramethylene glycols which are obtained, forexample, by the acidic polymerization of tetrahydrofuran and which havemolecular weights in the range from 200 to 6,000 and preferably in therange from 400 to 4,000.

Other suitable polyols are the liquid polyesters which can be obtainedby condensation of di- or tricarboxylic acids, for example adipic acid,sebacic acid, glutaric acid, with low molecular weight diols or triolssuch as, for example, ethylene glycol, propylene glycol, diethyleneglycol, triethylene glycol, dipropylene glycol, butane-1,4-diol,hexane-1,6-diol, glycerol or trimethylol propane.

Another group of polyols which may be used in accordance with theinvention are polyesters based on ε-caprolactone which are also known as"polycaprolactones".

However, polyester polyols of oleochemical origin may also be used.Oleochemical polyester polyols may be obtained, for example, by completering opening of epoxidized triglycerides of a fatty acid mixturecontaining at least partly olefinically unsaturated fatty acids with oneor more alcohols containing 1 to 12 carbon atoms and subsequent partialtransesterification of the triglyceride derivatives to alkyl esterpolyols containing 1 to 12 carbon atoms in the alkyl group (see, forexample, DE-A-3 626 223). Other suitable polyols are polycarbonatepolyols and dimer diols (Henkel KGaA) and, in particular, castor oil andderivatives thereof. Hydroxyfunctional polybutadienes, for example ofthe type commercially available under the name of "Poly-bd", may also beused as polyols for the compositions according to the invention.

Preferred diisocyanates or polyisocyanates are aromatic isocyanates, forexample diphenyl methane diisocyanate either in the form of the pureisomers, as a mixture of the 2,4'-/4,4'-isomers or even in the form ofdiphenyl methane diisocyanate (MDI) liquefied with carbodiimide which iscommercially available, for example, under the name of Isonate 143 L.So-called "crude MDI", i.e. the isomer/oligomer mixture of MDI which iscommercially available, for example, under the name of PAPI or DesmodurVK, may also be used. So-called "quasi-prepolymers", i.e. products ofthe reaction of MDI or toluene diisocyanate (TDI) with low molecularweight diols such as, for example, ethylene glycol, diethylene glycol,propylene glycol, dipropylene glycol or triethylene glycol, may also beused. Although the isocyanates mentioned above are the particularlypreferred isocyanates, aliphatic and cycloaliphatic diisocyanates orpolyisocyanates, for example hydrogenated MDI (H₁₂ MDI), tetramethylxylylene diisocyanate (TMXDI),1-isocyanatomethyl-3-isocyanato-1,5,5-trimethyl cyclohexane (IPDI),hexane-1,6-diisocyanate (HDI), the biuretization product of HDI, theisocyanuratization product of HDI or dimer fatty acid diisocyanate, mayalso be used in special cases.

Although a preferred embodiment of the compositions according to theinvention is catalyst-free, catalysts may also be used. Suitablecatalysts are any of the usual organometallic compounds known inpolyurethane chemistry such as, for example, iron compounds and, inparticular, tin compounds. Examples of such compounds are 1,3-dicarbonylcompounds of iron, such as iron(III) acetyl acetonate, and in particularthe organotin compounds of divalent and tetravalent tin, more especiallythe Sn(II) carboxylates and the dialkyl Sn(IV) dicarboxylates or thecorresponding dialkoxylates, for example dibutyl tin dilaurate, dibutyltin diacetate, dioctyl tin diacetate, dibutyl tin maleate, tin(II)octoate, tin(II) phenolate or even the acetyl acetonates of divalent andtetravalent tin. Other suitable catalysts are the highly active tertiaryamines or amidines which may optionally be used in combination with thetin compounds mentioned above. Suitable amines are both acyclic and, inparticular, cyclic compounds, for example tetramethyl butane diamine,bis(dimethylaminoethyl)-ether, 1,4-diazabicyclooctane (DABCO),1,8-diazabicyclo-(5.4.0)-undecene, 2,2'-dimorphol inodiethyl ether ordimethyl piperazine or even mixtures of the above-mentioned amines.

In addition, the adhesive according to the invention may optionallycontain stabilizers. Stabilizers in the context of the present inventionare antioxidants, UV stabilizers or hydrolysis stabilizers. The choiceof these stabilizers is determined on the one hand by the maincomponents of the composition and, on the other hand, by the applicationconditions and by the loads which the bond, joint or encapsulation isexpected to withstand. If the polyurethane prepolymer is made uppredominantly of polyether units, antioxidants--optionally incombination with UV stabilizers--are mainly required. Examples ofsuitable antioxidants are any of the commercially available stericallyhindered phenols and/or thioethers and/or substituted benzotriazolesand/or amines of the HALS type (hindered amine light stabilizer).

If the polyurethane prepolymer is essentially made up of polyesterunits, hydrolysis stabilizers, for example of the carbodiimide type, arepreferably used.

In addition, the compositions according to the invention may containother auxiliaries and additives known per se, for example plasticizers(such as phthalic acid esters) or additional thixotropicizing agents(for example Bentone, urea derivatives, fibrillated or pulped choppedfibers) or pigment pastes or pigments.

The polyols and the polyisocyanates are preferably used as atwo-component system, the so-called resin component containing thepolyols and also the fillers, the highly disperse silica and,optionally, drying agents. Suitable drying agents are any of the usualwater-binding agents such as, for example, monofunctional isocyanates,orthoformic acid esters and--in a particularly preferredembodiment--sodium aluminium silicates in the form of molecular sieves.

In general, the so-called hardener component only contains thediisocyanate or polyisocyanate or the "quasi-prepolymer", although thiscomponent, too, may optionally contain small quantities of fillers,thixotropicizing agents or pigments.

As mentioned at the beginning, the polyurethane compositions accordingto the invention may be used as adhesives, sealants and/or castingcompounds in a number of applications. They are particularly suitablefor assembly bonding and structural bonding, for example in themanufacture of sandwich elements.

Particularly preferred embodiments of the invention are described inmore detail in the following. The quantities mentioned in the are partsby weight unless otherwise indicated.

EXAMPLE 1 (Comparison Example)

Non-retarded catalyst-free polyurethane system

    ______________________________________                                                                % by weight                                           ______________________________________                                        Resin component                                                               Castor oil, OH value around 160                                                                         29.0                                                Polypropylene glycol, OH value around 240, trifunctional                                                5.0                                                 Na--Al silicate in castor oil (1:1 mixture)                                                             6.0                                                 Limestone flour, uncoated 20.5                                                Limestone flour, coated   39.5                                                Hardener component                                                            Diphenyl methane-4,4'-diisocyanate (crude MDI)                                                          100                                                 Mixing ratio of resin to hardener                                                                       6:1                                                 Pot life                  45      mins                                        Pot life after 8 weeks' separate storage of the resin and                                               37.5    mins                                        hardener components                                                           ______________________________________                                    

EXAMPLE 2 (Invention)

Retarded catalyst-free polyurethane system

    ______________________________________                                        Resin component                                                               ______________________________________                                        Castor oil, OH value around 160                                                                         29.0                                                Polypropylene glycol, OH value around 240, trifunctional                                                5.0                                                 Na--Al silicate in castor oil (1:1 mixture)                                                             6.0                                                 Limestone flour, uncoated 20.5                                                Limestone flour, coated   39.0                                                Aerosil 150               0.5                                                 Hardener component and mixing ratio as                                        in Example 1                                                                  Pot life                  60      mins                                        Pot life after storage for 8 weeks                                                                      60      mins                                        ______________________________________                                    

Comparison of Example 1 (Comparison Example) with Example 2 shows thatthe addition of Aerosil in accordance with the invention in Example 2does not lead to any change in pot life, even after 8 weeks' storage ofthe resin and hardener components. In addition, the pot life as a wholeis prolonged as required.

However, if only uncoated limestone flour is used as the filler, potlife cannot be influenced by the addition of Aerosil.

EXAMPLE 3 (Invention)

Accelerated catalyst-containing polyurethane system

    ______________________________________                                        Resin component                                                               ______________________________________                                        Castor oil                27.0                                                Polypropylene glycol, OH value around 240, trifunctional                                                3.0                                                 Na--Al silicate in castor oil (1:1 mixture)                                                             6.2                                                 Limestone flour, uncoated 49.475                                              Limestone flour, coated   13.5                                                Aerosil 200               0.8                                                 1,4-Diazabicyclo[2.2.2]octane (33.3% solution in                              dipropylene glycol)       0.025                                               Hardener component and mixing ratio                                           as in Example 1                                                               Pot life                  35      mins                                        Pot life after 12 weeks' storage                                                                        35      mins                                        ______________________________________                                    

This Example shows that, even in the case of catalyst-containingformulations, pot life remains constant after prolonged storage whereAerosil and at least partly coated filler are used in accordance withthe invention.

What is claimed is:
 1. A polyurethane composition of at least twocomponents, said components comprising at least one resin component andat least one hardener component, wherein the resin componentcomprises:castor oil, polypropylene glycol, Na--Al silicate, uncoatedlimestone flour, coated limestone flour, highly dispersed silica; andwherein the hardener component comprises:crude diphenylmethane-4,4'-diisocyanate.
 2. A polyurethane composition as in claim 1,wherein said resin component comprises:about 29% by weight castor oilhaving an OH value of about 160, about 5% by weight polypropylene glycolhaving an OH value of about 240, about 6% by weight Na--Al silicate incastor oil in a 1:1 mixture, about 20% by weight uncoated limestoneflour, about 39% by weight coated limestone flour, about 0.1% to about5% by weight highly dispersed silica; based on the weight of saidpolyurethane composition, and wherein the hardener componentcomprises:about 100% by weight diphenyl methane-4,4'-diisocyanate.
 3. Apolyurethane composition of at least two components, said componentscomprising at least one resin component and at least one hardenercomponent, wherein the resin component comprises:castor oil,polypropylene glycol, Na--Al silicate, uncoated limestone flour, coatedlimestone flour, highly dispersed silica,
 1. 4-Diazabicyclo[2.2.2]octanein a 33% solution in dipropylene glycol; andwherein the hardenercomponent comprises:crude diphenyl methane-4,4'-diisocyanate.
 4. Apolyurethane composition as in claim 3, wherein said resin componentcomprises:about 27% by weight castor oil having an OH value of about160, about 3% by weight polypropylene glycol having an OH value of about240, about 6% by weight Na--Al silicate in castor oil in a 1:1 mixture,about 50% by weight uncoated limestone flour, about 14% by weight coatedlimestone flour, about 0.1% to about 5% by weight highly dispersedsilica, about 0.03% by weight 1,4-Diazabicyclo[2.2.2]octane in a 33%solution in dipropylene glycol; based on the weight of said polyurethanecomposition, and wherein the hardener component comprises:about 100% byweight diphenyl methane-4,4'-diisocyanate.
 5. A multi-component systemsuitable for mixing to form a polyurethane composition, saidmulti-component system comprising(a) a resin component characterized byan absence of isocyanate and comprising:(i) at least one polyolcomprising liquid polyhydroxy compounds containing at least two hydroxylgroups per molecule; (ii) at least one filler selected from the groupconsisting of limestone flour, natural ground chalks, heavy spar,talcum, mica, clays, carbon black and mixtures thereof, wherein at least20% by weight of the filler is coated with a coating; (iii) at least onehydrophilic highly dispersed amorphous pyrogenic silica in an amounteffective to cause the polyurethane composition to exhibit a longer andmore constant pot life upon mixing after the resin component has beenstored for a period of time, and (b) a hardener component comprised ofat least one isocyanate selected from the group consisting ofdiisocyanates, polyisocyanates, and mixtures thereof.
 6. Themulti-component system of claim 5, wherein the polyol is selected fromthe group consisting of copolymers of ethylene oxide, copolymers ofpropylene oxide, polytetramethylene glycols, polyesters,polycaprolactones, polycarbonate polyols, dimer dials, hydroxyfunctionalpolybutadienes, hydroxyfunctional oils with an OH functionality of atleast two, difunctional polypropylene oxides, trifunctionalpolypropylene oxides, polyethylene oxides and mixtures thereof.
 7. Themulti-component system of claim 5, wherein at least one polyol is ahydroxyfunctional oil selected from the group consisting of castor oil,castor oil derivatives, and mixtures thereof.
 8. The multi-componentsystem of claim 5, wherein the resin component is comprised of at leastat least one hydroxyfunctional oil and at least one member selected fromthe group consisting of difunctional polypropylene oxides, trifunctionalpolypropylene oxides, polyethylene oxides, copolymers of ethylene oxide,and copolymers of propylene oxide.
 9. The multi-component system ofclaim 5, wherein said amount of the hydrophilic highly dispersedamorphous pyrogenic silica is about 0.1 to about 5% by weight, based onthe polyurethane composition as a whole.
 10. The multi-component systemof claim 5, wherein at least about 30% of the filler is coated.
 11. Themulti-component system of claim 5, wherein the coating is comprised of asubstance selected from the group consisting of long chain saturatedfatty acids, long chain unsaturated fatty acids, alkali metal salts oflong-chain saturated fatty acids, alkaline earth metal salts oflong-chain saturated fatty acids, alkali metal salts of long-chainunsaturated fatty acids, alkaline earth metal salts of long-chainunsaturated fatty acids, carboxylated polybutadienes, metal salts ofcarboxylated polybutadienes, esters of carboxylated polybutadienes,carboxylated poly-α-olefins, metal salts of carboxylated poly-α-olefins,esters of carboxylated poly-α-olefins, rosin acids, metal salts of rosinacids, esters of rosin acids and mixtures thereof.
 12. Themulti-component system of claim 5, wherein at least one isocyanate isselected from the group consisting of aromatic isocyanates, aliphaticisocyanates, cycloaliphatic isocyanates, dimer fatty acid diisocyanatesand mixtures thereof.
 13. The multi-component system of claim 5, whereinat least one isocyanate is an aromatic isocyanate selected from thegroup consisting of diphenyl methane diisocyanate, toluene diisocyanate,diphenyl methane diisocyanate liquified with carbodiumide, products ofthe reaction of toluene diisocyanate with low molecular weight diols,products of the reaction of diphenyl methane diisocyanate with lowmolecular weight diols and mixtures thereof.
 14. The multi-componentsystem of claim 5, wherein at least one isocyanate is an aliphaticisocyanate selected from the group consisting of hydrogenated diphenylmethane diisocyanate, hexane-1,6-diisocyanate, the biuretization productof hexane-1,6-diisocyanate, the isocyanuratization product ofhexane-1,6-diisocyanate and mixtures thereof.
 15. The multi-componentsystem of claim 5, wherein at least one isocyanate is a cycloaliphaticisocyanate selected from the group consisting of tetramethyl xylylenediisocyanate, 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane and mixtures thereof.
 16. The multi-component system ofclaim 5, wherein the resin component further comprises a drying agent.17. The multi-component system of claim 5, wherein said multi-componentsystem is catalyst-free.
 18. The multi-component system of claim 5,further comprising a catalyst.
 19. The multi-component system of claim18, wherein the catalyst is comprised of at least one member selectedfrom the group consisting of organotin compounds, tertiary amines,amidines, iron compounds and mixtures thereof.
 20. The multi-componentsystem of claim 5, further comprising at least one stabilizer.
 21. Amethod of prolonging and making more constant the pot life of apolyurethane composition obtained by mixing a multi-component systemcomprised of(a) a resin component characterized by an absence ofisocyanate and comprising:(i) at least one polyol comprising liquidpolyhydroxy compounds containing at least two hydroxyl groups permolecule; and (ii) at least one filler selected from the groupconsisting of limestone flour, natural ground chalks, heavy spar,talcum, mica, clays, carbon black and mixtures thereof, wherein at least20% by weight of the filler is coated with a coating; and (b) a hardenercomponent comprised of at least one isocyanate selected from the groupconsisting of diisocyanates, polyisocyanates, and mixtures thereof, saidmethod comprising incorporating in the resin component an effectiveamount of at least one hydrophilic highly dispersed amorphous pyrogenicsilica.
 22. The method of claim 21, wherein the polyol is selected fromthe group consisting of copolymers of ethylene oxide, copolymers ofpropylene oxide, polytetrametlylene glycols, polyesters,polycaprolactones, polycarbonate polyols, dimer diols, hydroxyfunctionalpolybutadienes, hydroxyfunctional oils with an OH functionality of atleast two, difunctional polypropylene oxides, trifunctionalpolypropylene oxides, polyethylene oxides and mixtures thereof.
 23. Themethod of claim 21, wherein the resin component comprises at least onehydroxyfunctional oil selected from the group consisting of castor oil,castor oil derivatives, and mixtures thereof.
 24. The method of claim21, wherein the hydrophilic highly dispersed amorphous pyrogenic silicais incorporated in an amount of about 0.1 to about 5% by weight, basedon the polyurethane composition as a whole.
 25. The method of claim 21,wherein the coating is comprised of a substance selected from the groupconsisting of long-chain saturated fatty acids, long chain unsaturatedfatty acids alkali metal salts of long-chain saturated fatty acids,alkaline earth metal salts of long-chain saturated fatty acids, alkalimetal salts of long-chain unsaturated fatty acids, alkaline earth metalsalts of long-chain unsaturated fatty acids, carboxylatedpolybutadienes, metal salts of carboxylate polybutadienes, esters ofcarboxylated polybutadienes, carboxylated poly-α-olefins, metal salts ofcarboxylated poly-α-olefins, esters of carboxylated poly-α-olefins,rosin acids, metal salts of rosin acids, esters of rosin acids andmixtures thereof.
 26. The method of claim 21, wherein the isocyanate isselected from the group consisting of aromatic isocyanates, aliphaticisocyanates, cycloaliphatic isocyanates, dimer fatty acid diisocyanatesand mixtures thereof.
 27. The method of claim 21, wherein the resincomponent further comprises a drying agent.
 28. The method of claim 21,wherein the multi-component system is catalyst-free.
 29. The method ofclaim 21, wherein the multi-component system further comprises acatalyst.
 30. The method of claim 29, wnerein the catalyst comprises atleast one member selected from the group consisting of organotincompounds, tertiary amines, amidines, iron compounds and mixturesthereof.
 31. The method of claim 21, further comprising at least onestabilizer.
 32. A multi-component system suitable for mixing to form apolyurethane composition, said multi-component system comprising(a) aresin component characterized by an absence of isocyanate andcomprising: (i) polyols comprising liquid polyhydroxy compoundscontaining at least two hydroxyl groups per molecule, wherein at leastone polyol is selected from the group consisting of copolymers ofpropylene oxide, polypropylene oxides, and mixtures thereof and at leastone polyol is a hydroxyfunctional oil,(ii) at least one filler selectedfrom the group consisting of limestone flour, natural ground chalks,heavy spar, talcum, mica, clays, carbon black and mixtures thereof,wherein at least 30% by weight of the filler is coated with a coating;(iii) at least one hydrophilic highly dispersed amorphous pyrogenicsilica in an amount of about 0.1 to about 5% by weight, based on thepolyurethane composition as a whole, and (iv) a drying agent; and (b) ahardener component comprised of at least one aromatic isocyanateselected from the group consisting of aromatic diisocyanates, aromaticpolyisocyanates, and mixtures thereof;wherein said polyurethanecomposition exhibits a longer and more constant pot life upon mixingafter being stored for a period of time than an analogous polyurethanecomposition which does not contain the hydrophilic highly dispersedamorphous pyrogenic silica.
 33. The multi-component system of claim 32,wherein the hardener component consists essentially of aromaticisocyanate.
 34. The multi-component system of claim 32, wherein at leastone polyol is a polypropylene glycol containing two or three hydroxylgroups per molecule.
 35. The multi-component system of claim 32, whereinthe hydroxyfunctional oil is selected from the group consisting ofcastor oil, castor oil derivatives, and mixtures thereof.
 36. Themulti-component system of claim 32, wherein said amount of thehydrophilic highly dispersed amorphous pyrogenic silica is about 0.3 toabout 3% by weight, based on the polyurethane composition as a whole.37. The multi-component system of claim 32, wherein the coating iscomprised of a long chain fatty acid or alkali metal or alkaline earthmetal salt thereof.
 38. The multi-component system of claim 32, whereinthe aromatic isocyanate comprises crude MDI.
 39. The multi-componentsystem of claim 32, wherein the drying agent is selected from the groupconsisting of monofunctional isocyanates orthoformic acid esters, sodiumaluminum silicates in the form of molecular sieves and mixtures thereof.40. The multi-component system of claim 32, wherein said multi-componentsystem is catalyst-free.
 41. The multi-component system of claim 32,further comprising a catalyst component comprising at least one memberselected from the group consisting of organotin compounds, tertiaryamines, amidines, iron compounds and mixtures thereof.
 42. The multicomponent system of claim 32, further comprising at least one stabilizerselected from the group consisting of antioxidants, UV stabilizers,hydrolysis stabilizers and mixtures thereof.
 43. The multi-componentsystem of claim 32, wherein at least one filler is a limestone flour.44. A method of prolonging and making more constant the pot life of apolyurethane composition obtained by mixing a multi-component systemcomprised of(a) a resin component characterized by an absence ofisocyanate and comprising:(i) polyols comprising liquid polyhydroxycompounds containing at least two hydroxyl groups per molecule, whereinat least one polyol is selected from the group consisting of copolymersof propylene oxide, polypropylene oxides, and mixtures thereof and atleast one polyol is a hydroxyfunctional oil; (ii) at least one fillerselected from the group consisting of limestone flour, natural groundchalks, heavy spar, talcum, mica, clays, carbon black and mixturesthereof, wherein at least 30% by weight of the filler is coated with acoating; and (iii) a drying agent; and (b) a hardener componentcomprised of at least one aromatic isocyanate selected from the groupconsisting of aromatic diisocyanates, aromatic polyisocyanates, andmixtures thereof; said method comprising incorporating into the resincomponent at least one hydrophilic highly dispersed amorphous pyrogenicsilica in an amount of about 0.1 to about 5% by weight, based on thepolyurethane composition as a whole.
 45. The method of claim 44, whereinthe hardener component consists essentially of aromatic isocyanate. 46.The method of claim 44, wherein at least one polyol is a polypropyleneglycol containing two or three hydroxyl groups per molecule.
 47. Themethod of claim 44, wherein the hydroxyfunctional oil is selected fromthe group consisting of castor oil, castor oil derivatives, and mixturesthereof.
 48. The method of claim 44, wherein said amount of thehydrophilic highly dispersed amorphous pyrogenic silica is about 0.3 toabout 3% by weight, based on the polyurethane composition as a whole.49. The method of claim 44, wherein the coating is comprised of a longchain fatty acid or alkali metal or alkaline earth metal salt thereof.50. The method of claim 44, wherein the aromatic isocyanate comprisescrude MDI.
 51. The method of claim 44, wherein the drying agent isselected from the group consisting of monofunctional isocyanates,orthoformic acid esters, sodium aluminum silicates in the form ofmolecular sieves and mixtures thereof.
 52. The method of claim 44,wherein the multi-component system is catalyst-free.
 53. The method ofclaim 44, wherein the multi-component system further comprises acatalyst comprising at least one member selected from the groupconsisting of organotin compounds, tertiary amines, amidines, ironcompounds and mixtures thereof.
 54. The method of claim 44, furthercomprising at least one stabilizer selected from the group consisting ofantioxidants, UV stabilizers, hydrolysis stabilizers and mixturesthereof.
 55. The method of claim 44, wherein at least one filler is alimestone flour.
 56. A process comprising a step for adhering, sealingor casting, wherein the multi-component system of claim 5 is mixed toform a polyurethane composition and said polyurethane composition isused in said step.
 57. A process comprising a step for adhering, sealingor casting, wherein the multi-component system of claim 32 is mixed toform a polyurethane composition and said polyurethane composition isused in said step.